The present invention relates to a method of cleaning a surface of a semiconductor wafer, and more particularly, to a method of effectively removing small particles on the surface of the semiconductor wafer and preventing a silicide layer on the semiconductor wafer from corroding.
A metal-oxide-semiconductor field effect transistor (MOSFET) is a very important device in integrated circuits. Electrical performance of a gate in the MOSFET is a critical factor influencing quality of the MOSFET:
The gate generally comprises a gate oxide layer, a polysilicon layer and a silicide layer. The silicide layer can be formed by utilizing a traditional chemical vapor deposition method or a self-aligned silicide method. After completing an etching process to define a gate on a surface of a silicon substrate, a cleaning process is performed to remove contaminants, such as organics, small particles or heavy metals, on the surface of the semiconductor wafer. As a result, the cleaning process can prevent those contaminants from reducing the electrical performance of the gate or quality control of semiconductor fabrication.
SC-1 solution is the most commonly used solution for removing contaminants on the surface of the semiconductor wafer. It is mainly comprised of hydrogen peroxide (H2O2) and ammonia (NH4OH). A prior art cleaning method of removing small particles on the surface of the semiconductor wafer is disclosed in U.S. Pat. No. 5,516,730, proposed by Pirooz et al. In the cleaning method of U.S. Pat. No. 5,516,730, a semiconductor wafer is immersed in a traditional SC-1 solution to remove organics and small particles. Further, heavy metals remaining on the surface of the semiconductor wafer form soluble complexes in the SC-1 solution. The cleaning process mentioned above is usually performed at a temperature exceeding 50xc2x0 C. Then, a solution containing a mixture of hydrofluoric acid and hydrochloric acid is utilized to moisten and rinse the semiconductor wafer. After that, deionized water is utilized to immerse the surface of the semiconductor wafer. Finally, an ozonated water is utilized to touch the surface of the semiconductor wafer.
However, the cleaning method proposed by Pirooz, et al. is not suitable for a semiconductor wafer covered by a silicide layer because SC-1 solution would seriously corrode the silicide layer on the semiconductor wafer. For example, a rate of silicide layer corrosion due to SC-1 solution exceeds 24 xc3x85/min at a temperature of 70xc2x0 C. The corrosion of the suicide layer leads to insufficient thickness of the silicide layer after many repetitions of cleaning processes. As a result, a Caros solution cleaning process is performed to clean the surface of the semiconductor wafer covered by the silicide layer.
The Caros solution cleaning process utilizes a sulfuric acid solution, whose volume ratio of sulfuric acid to water is about 5 to 1, to clean the surface of the semiconductor wafer at a temperature between 90xc2x0 C. and 125xc2x0 C. Utilizing the Caros solution to clean the surface of the semiconductor wafer does not lead to corrosion of the silicide layer. However, an ability of the Caros solution to remove small particles on the semiconductor wafer has not met requirements of more stringent semiconductor fabrication.
It is therefore a primary objective of the present invention to provide a method of cleaning a surface of a semiconductor wafer. The method utilizes an SC-1 solution comprising hydrogen peroxide (H2O2) and ammonia (NH4OH), and serving as a cleaning solution to remove small particles on the surface of the semiconductor wafer.
It is another objective of the present invention to provide a cleaning method that prevents a silicide layer of the semiconductor wafer from corroding. The method effectively removes small particles remaining on the surface of the semiconductor wafer to enhance a yield of semiconductor products.
In the method of the present invention, a temperature of the semiconductor wafer is controlled to between room temperature and 45xc2x0 C. Then, a cleaning solution (SC-1), with a temperature between 0xc2x0 C. and 45xc2x0 C., is utilized to clean the semiconductor wafer to effectively remove small particles remaining on the surface of the semiconductor wafer. The cleaning solution (SC-1) comprises a pre-determined volume ratio of hydrogen peroxide (H2O2), ammonia (NH4OH), and deionized water.
It is an advantage of the present invention that it provides a method of utilizing SC-1 solution to clean a semiconductor wafer covered by a silicide layer. By controlling a temperature, the silicide layer on the surface of the semiconductor wafer is prevented from corrosion by the SC-1 solution and, therefore, a particle-free surface of the semiconductor wafer is obtained.
These and other objectives and advantages of the present invention will no doubt become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.